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arXiv:2303.14943 · Physical Review Letters

Testing Genuine Multipartite Nonlocality via an Inflated Network with Multicopy Entangled States

Qian-Xi Zhang, Ming-Xing Luo, Ya-Li Mao, Hu Chen, Yu-Hang Yao, Zhi-Lian Liu, Shao-Ming Fei, Xue Yang, Zheng-Da Li

Published May 13, 2026• 0 citations
arXivHTMLPDF

Abstract

Understanding the nonlocality of multipartite quantum systems provides valuable insights into their behaviors and potential applications. In this Letter, assuming a quantum network inflated with multiple copies of genuine multipartite entangled states, we propose a novel noise-robust approach to test the genuine multipartite nonlocality inherent in each copy under Svetlichny's biseparable model. This extends Gisin's theorem to an arbitrary number of parties, establishing the equivalence among genuine multipartite nonlocality, genuine multipartite steering, and genuine multipartite entanglement for all multipartite pure states under the multiple copies assumption. In the experiment, we employ a hybrid photonic quantum network to verify the genuine tripartite nonlocality of generalized Greenberger-Horne-Zeilinger and W states beyond previously explored parameter regimes. This Letter not only offers a unified robust method on exploring multipartite quantum correlations, but also opens a new avenue for studying genuine multipartite nonlocality through network-distributed multicopy quantum states and different network topologies.

DOI
10.1103/mwxx-ln9v

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Understanding the nonlocality of multipartite quantum systems provides valuable insights into their behaviors and potential applications. In this Letter, assuming a quantum network inflated with multiple copies of genuine multipartite entangled states, we propose a novel noise-robust approach to test the genuine multipartite nonlocality inherent in each copy under Svetlichny's biseparable model. This extends Gisin's theorem to an arbitrary number of parties, establishing the equivalence among genuine multipartite nonlocality, genuine multipartite steering, and genuine multipartite entanglement for all multipartite pure states under the multiple copies assumption. In the experiment, we employ a hybrid photonic quantum network to verify the genuine tripartite nonlocality of generalized Greenberger-Horne-Zeilinger and W states beyond previously explored parameter regimes. This Letter not only offers a unified robust method on exploring multipartite quantum correlations, but also opens a new avenue for studying genuine multipartite nonlocality through network-distributed multicopy quantum states and different network topologies.
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Quantum entanglement and nonlocality are inextricably linked. However, while entanglement is necessary for nonlocality, it is not always sufficient in the standard Bell scenario. We derive sufficient conditions for entanglement to give rise to genuine multipartite nonlocality in networks. We find that any network where the parties are connected by bipartite pure entangled states is genuine multipartite nonlocal, independently of the amount of entanglement in the shared states and of the topology of the network. As an application of this result, we also show that all pure genuine multipartite entangled states are genuine multipartite nonlocal in the sense that measurements can be found on finitely many copies of any genuine multipartite entangled state to yield a genuine multipartite nonlocal behavior. Our results pave the way toward feasible manners of generating genuine multipartite nonlocality using any connected network.
Sharing genuine multipartite entanglement by considering collective use of copies of biseparable states, which are entangled across all bipartitions but lack genuine multipartite entanglement at the single-copy level, plays a central role in several quantum information processing protocols, and has been referred as genuine multipartite entanglement activation. We present a protocol for three-qutrit systems showing that two copies of rank-two biseparable states, entangled across every bipartition, are sufficient to generate a genuinely multipartite entangled state with nonzero probability. This contrasts with the three-qubit scenario where many copies of biseparable states might be required for sharing genuine multipartite entanglement. We subsequently generalize our protocols to the case of an arbitrary number of parties. Interestingly, the proposed construction naturally leads to the activation of genuinely nonlocal correlations, yielding a result that is stronger than genuine multipartite entanglement activation alone.
Multipartite quantum nonlocality is an important diagnostic tool and resource for both researches in fundamental quantum mechanics and applications in quantum information protocols. Shared reference frames among all parties are usually required for experimentally observing quantum nonlocality, which is not possible in many circumstances. Previous results have shown violations of bipartite Bell inequalities with approaching unit probability, without shared reference frames. Here we experimentally demonstrate genuine multipartite quantum nonlocality without shared reference frames, using the Svetlichny inequality. A significant violation probability of 0.58 is observed with a high-fidelity three-photon Greenberger-Horne-Zeilinger state. Furthermore, when there is one shared axis among all the parties, which is the usual case in fiber-optic or earth-satellite links, the experimental results demonstrate the genuine three-partite nonlocality with certainty. Our experiment will be helpful for applications in multipartite quantum communication protocols.
Abstract We propose an optimal and efficient numerical test for witnessing genuine multipartite nonlocality based on a geometric approach. In particular, we consider two non-equivalent models of local hidden variables, namely the Svetlichny and the no-signaling bilocal models. While our knowledge concerning these models is well established for Bell-type scenarios involving two measurement settings per party, the general case based on an arbitrary number of settings is a considerably more challenging task and very little work has been done in this field. In this paper, we applied such general tests to detect and characterize genuine n-way nonlocal correlations for various states of three qubits and qutrits. Apart from the fundamental problem of characterizing genuine multipartite nonlocal correlations, the extension of the number of measurements beyond two is also of practical importance. As a measure of nonlocality, we use the probability of violation of local realism under randomly sampled observables, and the strength of nonlocality, described by the resistance to white noise admixture. In particular, we analyze to what extent the Bell-type scenario involving two measurement settings can be used to certify genuine n-way nonlocal correlations generated for more general models. In addition, we propose a simple procedure to detect such nonlocal correlations for randomly chosen settings with an efficiency of up to 100%. Due to its near-perfect efficiency, our method may open new possibilities in device-independent quantum cryptography applications where strong nonlocality between all partners is required.